It is well known that vacuum cleaners, such as upright vacuums, may use a rotating brushroll to help clean various surfaces, such as carpeting. Canister type vacuum cleaners may also use a power head having a rotating brushroll, as is known in the art. The brushroll typically rotates about a horizontal axis and provides surface agitation to release dirt and dust trapped in and upon the surface being cleaned. Once agitated, the dirt and dust are sucked into the vacuum cleaner through the dirty air inlet. Suction force is typically generated by a fan motor unit.
The brushroll is typically driven by a motor. The vacuum may have one motor that provides both suction and drive power for the brushroll (a so-called “single-motor” vacuum). Alternatively, the vacuum may have two motors—one for generating suction and one for driving the brushroll. Such a “two-motor” vacuum configuration may have the drawback of increased weight and cost, but may be favored where separate control of the suction fan and brushroll are desired, or the fan motor is for some reason not capable of driving the brushroll. Power from a motor, in any configuration, must be transferred from the motor to the brushroll. The brushroll may be driven at a slower rotational speed than the motor. For example, a motor may operate at over 10,000 revolutions per minute (rpm), and it may be desirable to rotate the brushroll at a slower speed, such as 3,000 rpm. As is known in the art, a drive belt is typically used for driving the brushroll. The belt typically is a high strength, long life belt that may be flat or ridged or toothed. A reduction gear and clutch mechanism may be provided. A cogged belt and/or reduction gears also may be used to provide gearing reduction. Some vacuums may alternatively use a direct drive from the motor to the brushroll, or incorporate the motor in the brushroll.
While brushrolls are commonly used and typically beneficial, they present a potential problem in that the brushroll may continue to rotate even when it is not desirable. For example, rotation may continue when the vacuum is stopped or placed into an upright position with the power still on, or when cleaning smooth floors that may not benefit from a brushroll. In fact, damage to the surface below the rotating brushroll may result from the brushroll rotating in one place. For example, carpet fibers may become worn or burned from frictional heat generated from the continuous rotation of the brushroll over a small part of the carpet. In a typical single-motor vacuum with a direct drive brushroll, there may be no independent control over the brushroll, such that in order to stop the brushroll, the vacuum itself may need to be turned off. Some single-motor vacuums may incorporate a lifting mechanism for the brushroll, which lifts the brushroll off the floor when the vacuum is placed in the upright position or when it is desired to clean smooth floors, but the rotation of the brushroll may continue. In other designs, an idler pulley configuration may be used, in which the drive belt is placed upon an idler pulley when the vacuum is placed in the upright position or when it is desired to clean smooth floors, stopping the brushroll rotation. In such devices, the driven belt must be replaced upon the driven pulley to resume operation, which often requires a mechanically complex and potentially unreliable mechanism to disengage and engage the brushroll. In other cases, a clutch mechanism may be used to disengage the brushroll.
Two-motor vacuum cleaners have potential to provide greater control over when the brushroll is rotating, because the brushroll motor can be operated by manually or automatically operated switches to turn the brushroll on and off independently of the vacuum source motor. Such devices can be heavier and more expensive than single-motor vacuums.
Another potential problem with brushrolls is that they can become jammed. For example, a foreign object may become lodged into the brushroll and prevent rotation. When this happens, the drive motor could overheat (particularly if the motor stops when the brushroll stops) and/or the drive belt or other drive mechanisms could be damaged. During such jams, it is desirable to disengage or stop drive power to the brushroll to prevent damage to the vacuum or the foreign object. Some vacuums use thermally-operated switches to cut off power to the motor when an overheating condition is reached. Other vacuums use a non-replaceable fuse that renders the vacuum inoperative and irreparable if the motor locks. The vacuum also may be designed with the belt as the weakest link, so that the belt typically fails during a severe jam condition. Still other vacuums use a clutch mechanism which may disengage or slip under a high torque condition.
Different clutch mechanisms are known in the art. Clutch mechanisms are used to provide both a power transfer function and a torque limiting function through the use of various structural configurations, such as friction plates, flexible couplings, springs, detent plates, wave plates, and magnetic couplings. Exemplary clutch mechanisms with application to vacuums incorporating some of the aforementioned features are described in U.S. Pat. Nos. 3,228,209; 3,797,621; 4,235,321; 4,532,667; 4,766,641; 5,601,491; 6,691,849; and 7,228,593; which references are incorporated herein.
It has been found that many different requirements may be desired of vacuum cleaner brushroll drive and clutch mechanisms. For example, such requirements sometimes include: operate in the overload condition for a long time without overheating; survive numerous disengagement and reengagement cycles; operate automatically to address different cleaning modes (e.g., turn off the brushroll during accessory cleaning operations and when vacuuming on bare floors); operate manually to allow the user to selectively disengage the brushroll; operate in dusty environments; and so on. Some of these requirements may oppose one another in various respects. For example, it is desirable to provide a brushroll overload clutch that will disengage drive torque to the brushroll immediately upon reaching an overload torque value, to better protect any objects that contact the brushroll, the brushroll, and the drive components. While this could be accomplished using an overload clutch having a relatively low overload torque value, the clutch may be so sensitive that it will disengage when it is not desired, such as when the brushroll is started on thick carpets or moved rapidly from a smooth surface to a carpeted surface.
While various prior art devices, such as those described above, have been used, there exits a need to provide alternatives to such devices.